A known apparatus for the continuous casting of metal includes a cooled, generally vertical, open-ended mold. Molten metal is continuously admitted into the mold form a suitable teeming vessel such as a tundish. The molten metal adjacent the walls of the mold solidifies thereby forming a shell with a molten core. The shell and its molten core are continuously withdrawn from the mold thus producing a long strand which, after complete solidification, is cut into lengths and then further processed.
In order to reduce the height of the apparatus, the strand is conveyed along a path which curves towards the horizontal. a straightener is located adjacent the point at which the transition from a vertical to a horizontal orientation is complete and straightens the strand which would otherwise maintain its curvature. After straightening, the strand is cut into lengths which are eventually conveyed to a mill for further processing.
It is necessary for the strand to be completely solidified before the cutting operation since otherwise molten metal will flow onto the casting apparatus and cause damage. Generally, it is attempted to obtain complete solidification prior to the straightening operation so as to eliminate the chance that the shell will rupture during straightening and permit molten metal to escape.
In order to solidify the strand throughout its cross-section, the strand is subjected to the direct action of cooling fluid sprays, typically water sprays, between the exit end of the mold and the entrance to the straightener. To this end, spray nozzles are arranged above and below the strand as well as to the sides of the strand. The direct cooling of the strand between the mold and the straightener is referred to as "secondary" cooling to distinguish it from the indirect, "primary" cooling which takes place at the walls of the mold. The zone between the mold and the straightener is correspondingly referred to as the "secondary cooling zone."
The distance between the mold and the straightener is relatively long and the length which can be sprayed by any one nozzle is limited. Accordingly, it is necessary to arrange a substantial number of nozzles along the length of the secondary cooling zone, both above and below the strand as well as to the sides thereof.
Inasmuch as underspraying or overspraying can be detrimental from a metallurgical point of view, the various nozzles must be correctly aligned. Due to the large number of nozzles, the alignment procedure is a time-consuming one. This problem is magnified for rectangular strands having a large width, i.e. slabs which have wide upper and lower surfaces. One reason resides in the inability of a single nozzle to spray across the entire width of such a strand. Thus, aside from the large number of nozzles which are in any event arranged along the length of the secondary cooling zone, one or more additional nozzles must be provided for each of the wide surfaces of the strand at every spraying location along this length. In other words, two or more nozzles directed at the wide surfaces of the strand are arranged side-by-side at each spraying location. The increased number of nozzles necessary here increases the alignment difficulties. Another reason that alignment problems are greater for strands of large width resides in that the casting apparatus is more complicated thereby hampering access to the nozzles.
An additional difficulty with the early prior art nozzles stems from the fact that it is necessary to position the nozzles relatively close to the strand in order to avoid overspraying. The close proximity of the nozzles to the strand makes them susceptible to damage in the event that the shell of the strand ruptures thereby permitting molten metal to escape.
In order to reduce the number of nozzles required to cool a rectangular strand of large width, it has been proposed to spray the wide surfaces of such a strand using a nozzle having an outlet opening in the form of a rectangular slot. The slot extends transversely to the longitudinal axis of the strand and is bounded by a pair of faces which extend perpendicular to the longitudinal axes of the strand and nozzle. These faces control the thickness of the spray pattern which is bounded by a pair of parallel lines extending transversely of the strand.
This slotted nozzle is capable of spraying greater widths than earlier prior art nozzles. Consequently, the plurality of nozzles arranged side-by-side at each spraying location along the secondary cooling zone may be replaced by a single slotted nozzle. The slotted nozzle may also be positioned farther away from the strand than the earlier nozzles thereby reducing the chances of damage to the nozzle in the event that the shell of the strand ruptures.
Although the slotted nozzle provides a good solution to the above problems for the spraying of the wide upper and lower surfaces of a large rectangular strand, it cannot satisfactorily spray the sides of a curved strand. Consequently, it neither permits a reduction in the number of nozzles required for spraying the sides of a curved strand nor overcomes the proximity problem for the nozzles used to spray such sides. Moreover, for narrow strands such as billets which require only a single nozzle for each surface at any spraying location along the secondary cooling zone, the slotted nozzle results in no reduction whatsoever in the number of nozzles.